Abstract ? Project 3: Enhancing antigen and cytokine expression to break immune tolerance and improve antitumor response Gliomas, like other solid tumors, restrict immune recognition of aberrant cancer cells. Further complicating this, pediatric cancers also have lower mutation rates than adult tumors making them more difficult to generate an immunotherapeutic response. This proposal addresses three mechanisms contributing to immune resistance in pediatric tumors: 1) low mutational loads, 2) myeloid immunosuppressive environment, and 3) MHC downregulation (immuno-editing). We have developed a multimodal virus based vaccine platform that uses the virus's natural ability to recruit immune cells and break immune tolerance to improve immune activity against the tumor. By encoding tumor associated self-antigens within the viral genome so that they are expressed during infection our results show that we can convert the antiviral response into an anti-tumor response. The studies described in our proposal seek to improve our virus-based multi-modal vaccine approach to overcome immune restriction in one of the most difficult to treat solid tumors, malignant glioma. We propose testing our hypothesis that: Engineered viral modifications that enhance native and adoptive immune cell activity will improve durable anti-tumor activity in treatment resistant pediatric gliomas by the following aims. Aim 1: To improve the immune mediated antitumor response through virus based tumor associated Fetal Antigen (TAFA) expression. Hypothesis: Viral based TAFA expression enhances T cell activity against tumor proteins and will extend anti-tumor activity after viral replication ceases. Aim 2: To promote antigen presentation and a durable anti-tumor immune response. Hypothesis: Engineering high affinity antigens will enhance their uptake in tumor associated macrophages and improve the durable anti-tumor response. Aim 3: To enhance antitumor activity by combining cytotoxic cellular therapies with oncolytic HSVs that improve immune cell recruitment and activity. Hypothesis: Viruses that enhance cytotoxic cellular therapy recruitment and activity will improve anti-tumor effect in the immunoedited tumor environment Impact: If successful, this flexible multimodal viral vaccine platform will harness and direct the immune stimulatory properties of a next generation oHSV in combination with cellular immune therapies to enhance their activity against low mutational load immunotherapy-resistant tumors and thus fits well into the aims of the Pediatric Immunotherapy Drug and Development Network (PI-DDN).